09391 Abstracts Collection -- Algorithms and Complexity for Continuous Problems

From 20.09.09 to 25.09.09, the Dagstuhl Seminar 09391 Algorithms and Complexity for Continuous Problems was held in the International Conference and Research Center (IBFI), Schloss Dagstuhl. During the seminar, participants presented their current research, and ongoing work and open problems were discussed. Abstracts of the presentations given during the seminar are put together in this paper. The first section describes the seminar topics and goals in general. Links to extended abstracts or full papers are provided, if available

Astronomical catalog desk reference, 1994 edition

The Astronomical Catalog Desk Reference is designed to aid astronomers in locating machine readable catalogs in the Astronomical Data Center (ADC) archives. The key reference components of this document are as follows: A listing of shortened titles for all catalogs available from the ADC (includes the name of the lead author and year of publication), brief descriptions of over 300 astronomical catalogs, an index of ADC catalog numbers by subject keyword, and an index of ADC catalog numbers by author. The heart of this document is the set of brief descriptions generated by the ADC staff. The 1994 edition of the Astronomical Catalog Desk Reference contains descriptions for over one third of the catalogs in the ADC archives. Readers are encouraged to refer to this section for concise summaries of those catalogs and their contents

Comparison of heavy-ion transport simulations: Collision integral with pions and Δ resonances in a box

We compare ten transport codes for a system confined in a box, aiming at improved handling of the production of $\Delta$ resonances and pions, which is indispensable for constraining high-density symmetry energy from observables such as the $\pi^-/\pi^+$ yield ratio in heavy-ion collisions. The system in a box is initialized with nucleons at saturation density and at 60 MeV temperature. The reactions $NN\leftrightarrow N\Delta$ and $\Delta\leftrightarrow N\pi$ are implemented, but the Pauli blocking and the mean-field potential are deactivated in the present comparison. Results are compared to those from the two reference cases of a chemically equilibrated ideal gas mixture and of the rate equation. In the results of the numbers of $\Delta$ and $\pi$, deviations from the reference values are observed in many codes, and they depend significantly on the size of the time step. These deviations are tied to different ways in ordering the sequence of collisions and decays, that take place in the same time step. Better agreements are seen in the reaction rates and the number ratios among the isospin species of $\Delta$ and $\pi$. These are, however, affected by the correlations, which are absent in the Boltzmann equation, but are induced by the way particle scatterings are treated in transport calculations. The uncertainty in the transport-code predictions of the $\pi^-/\pi^+$ ratio for the system initialized at n/p = 1.5, after letting the existing $\Delta$ resonances decay, is found to be within a few percent, which is sufficiently small so that it does not strongly impact constraining the high-density symmetry energy from heavy-ion collisions. Most of the sources of uncertainties have been understood, and individual codes may be further improved. This investigation will be extended in the future to heavy-ion collisions to ensure the problems identified here remain under control.Comment: 36 pages, 27 figures; a new Fig. 21 and revised results from some codes, achieving improved and consistent understandin

Passive planar terahertz retroreflectors

As the application of the Terahertz (THz) band (0.1 - 10 THz) is investigated in various settings, wireless communication stands out as an important frontier to explore. The benefits of increased bandwidth and data rates it promises will only be realized if new technology is developed to support it. Specifically, since THz wireless communication links are typically line-of-sight (LoS), the LoS can be blocked by moving obstacles, thereby requiring alternative link paths. One proposed solution for indoor wireless communications involves systems of steerable antennas, reflective wallpaper , and steerable mirrors which would redirect THz beams around a blocking obstacle. As an initial step in developing steerable mirrors for THz wireless systems, this thesis describes the development of a passive planar terahertz retroreflector based on the Van Atta array. The retroreflector is optimized and simulated using FEM software, fabricated via a low-cost additive manufacturing method, and characterized using terahertz time-domain spectroscopy. Comparison to a flat metal plate shows an increase in monostatic RCS for off-normal angles of incidence

Comparison of heavy-ion transport simulations: Collision integral in a box

Simulations by transport codes are indispensable to extract valuable physical information from heavy-ion collisions. In order to understand the origins of discrepancies among different widely used transport codes, we compare 15 such codes under controlled conditions of a system confined to a box with periodic boundary, initialized with Fermi-Dirac distributions at saturation density and temperatures of either 0 or 5 MeV. In such calculations, one is able to check separately the different ingredients of a transport code. In this second publication of the code evaluation project, we only consider the two-body collision term; i.e., we perform cascade calculations. When the Pauli blocking is artificially suppressed, the collision rates are found to be consistent for most codes (to within 1 % or better) with analytical results, or completely controlled results of a basic cascade code. In orderto reach that goal, it was necessary to eliminate correlations within the same pair of colliding particles that can be present depending on the adopted collision prescription. In calculations with active Pauli blocking, the blocking probability was found to deviate from the expected reference values. The reason is found in substantial phase-space fluctuations and smearing tied to numerical algorithms and model assumptions in the representation of phase space. This results in the reduction of the blocking probability in most transport codes, so that the simulated system gradually evolves away from the Fermi-Dirac toward a Boltzmann distribution. Since the numerical fluctuations are weaker in the Boltzmann-Uehling-Uhlenbeck codes, the Fermi-Dirac statistics is maintained there for a longer time than in the quantum molecular dynamics codes. As a result of this investigation, we are able to make judgements about the most effective strategies in transport simulations for determining the collision probabilities and the Pauli blocking. Investigation in a similar vein of other ingredients in transport calculations, like the mean-field propagation or the production of nucleon resonances and mesons, will be discussed in the future publications

BEACH MORPHODYNAMICS AND ASSOCIATED HAZARDS IN THE UK

In this thesis the relationship between beach morphodynamics and recreational hazards was investigated for the first time within the United Kingdom (UK). Four field experiments, conducted during 2006-2008 provided new insights into the spatio-temporal dynamics of UK beach types and their associated hazard signatures. The extent of data collection ranged from national (UK beach classification) to regional (temporal morphologic variation) to site specific (macrotidal rip current dynamics). Detailed morphodynamic characteristics of 98 beaches within the UK were collected. Twelve distinct beach groups were identified through cluster analysis, each having a unique morphodynamic signature. Conceptualisation within a relative two-dimensional framework using the dimensionless fall velocity (Q) and the relative tide range (RTR) required an absolute wave energy flux threshold to differentiate between intermediate beaches with (H2T > 5) and without (H2T < 5) three-dimensional bar morphology. The role of geologic control, sediment abundance and drainage characteristics in constraining beach morphodynamics was shown to be significant within the sites studied. Rip currents were responsible for 68% of all recorded incidents between 2005-2007 throughout all 76 beaches patrolled by the Royal National Lifeboat Institution (RNLI). Hazard type and severity varied between morphodynamic beach types. Intermediate beaches with low-tide bar/rip morphology (Q = 2-5 and RTR < 7), including Low-Tide Terrace and Rip (LTT+R) and Low-tide Bar/Rip (LTBR) beaches, presented the greatest risk to the insea beach user. These high risk beaches, representing 59% of the west coast beaches in Devon and Cornwall, also attracted the greatest visitor populations. Seasonal monitoring of hydrodynamics and morphology at LTT+R and LTBR beaches in Devon and Cornwall (annual Hsio% = 3-4 m; mean spring tidal range = 4.2-8.6 m) identified key mechanisms controlling the temporal hazard signature (THS), a term used here to describe the spatio-temporal variation in type and severity o f bathing hazard within a specified region both in the alongshore as well as in the cross-shore (significant in macrotidal environments). The morphological template controlled the presence, extent and intensity of beach rip current systems, where the development of low/tide transverse and inter-tidal bar/rip systems during summer presented the greatest morphological hazard. Typical summer wave forcing by relatively small, long period swell {H, - 0.5-1 m; Tp ~ 6-10 s) over this morphology provided conditions conducive to hazardous rip currents. Under these conditions hazard exposure was increased due to the accessibility of the relatively low energy surf zone. Both spring/neap and semi-diurnal tidal variations were identified as key controls on the THS. Variable tidal excursion modulates rip current activity, and tidal translation rates control the rate of change of the THS. The 'optimum' combination of these mechanisms results in the 'switching' on and off of rip currents during spring low tides and the subsequent rapid alongshore migration of rip channel/hazard location as the surf zone inundates the landward inter-tidal bar system. In conjunction with high insea population, these 'optimum hazard scenarios' drove the high risk, coast-wide 'mass rescue' events identified in the incident records. This work provides a scientific, standardised basis for a beach risk assessment model and lifeguard training programs within the RNLI. Improved understanding of macrotidal rip currents has initiated new field and modelling efforts to further general quantitative understanding of these systems, vital to the improvement of beach safety services.Royal National Lifeboat Institutio

Morphology of coronal mass ejections between the sun and the earth

The theme of my PhD has been to investigate the global shape and size of coronal mass ejections, or CMEs, as they propagate from the Sun towards the Earth. CMEs are large eruptive events originating from previously magnetically confined structures in the solar atmosphere. These phenomena are the single biggest drivers for geomagnetic disturbances at Earth. My research is focused on analysing spacecraft data obtained both by imaging observations and in situ instrumentation. The three pieces of work presented in this thesis are summarised below: Using the NASA STEREO mission, launched in 2006, I have analysed data from the Heliospheric Imager (HI) instruments. This new instrument is uniquely positioned to observe CMEs as they propagate away from the Sun into the inner heliosphere between 0.1 and 1 AU. Using this data I have been able to estimate the radial expansion of a single CME as it propagates in the inner heliosphere. Investigating another case study event seen by STEREO-B in November 2007, I have been able to show that the distortion of a CME can be directly attributed to a structured solar wind. By using a 3D MHD simulation of the solar wind in the vicinity of the CME, it has been shown that a bimodal velocity structure within this solar wind was driving the CME from behind and distorting it from a circular to a concave morphology. Using in situ data, I have also attempted to deduce the shape of CMEs in the inner heliosphere. To do this I analysed the shock wave driven ahead of the propagating CME, applying a technique previously used to predict the distance of the shock upstream of Earth’s magnetosphere - this distance can be predicted when the object’s shape (Earth) is known. I have carried out a statistical survey of many CMEs over a range of distances from the Sun, and compared them to theoretical predictions of their shape based on geometry

Novel neural approaches to data topology analysis and telemedicine

1noL'abstract è presente nell'allegato / the abstract is in the attachmentopen676. INGEGNERIA ELETTRICAnoopenRandazzo, Vincenz

A Comprehensive Analysis Of Clouds, Radiation, And Precipitation In The North Pacific Itcz In The NASA GISS Modele GCM And Satellite Observations

Global circulation/climate models (GCMs) remain as an invaluable tool to predict future potential climate change. To best advise policy makers, assessing and increasing the accuracy of climate models is paramount. The treatment of clouds, radiation and precipitation in climate models and their associated feedbacks have long been one of the largest sources of uncertainty in predicting any potential future climate changes. Three versions of the NASA GISS ModelE GCM (the frozen CMIP5 version [C5], a post-CMIP5 version with modifications to cumulus and boundary layer turbulence parameterizations [P5], and the most recent version of the GCM which builds on the post-CMIP5 version with further modifications to convective cloud ice and cold pool parameterizations [E5]) have been compared with various satellite observations to analyze how recent modifications to the GCM has impacted cloud, radiation, and precipitation properties. In addition to global comparisons, two areas are showcased in regional analyses: the Eastern Pacific Northern ITCZ (EP-ITCZ), and Indonesia and the Western Pacific (INDO-WP). Changes to the cumulus and boundary layer turbulence parameterizations in the P5 version of the GCM have improved cloud and radiation estimations in areas of descending motion, such as the Southern Mid-Latitudes. Ice particle size and fall speed modifications in the E5 version of the GCM have decreased ice cloud water contents and cloud fractions globally while increasing precipitable water vapor in the model. Comparisons of IWC profiles show that the GCM simulated IWCs increase with height and peak in the upper portions of the atmosphere, while 2C-ICE observations peak in the lower levels of the atmosphere and decrease with height, effectively opposite of each other. Profiles of CF peak at lower heights in the E5 simulation, which will potentially increase outgoing longwave radiation due to higher cloud top temperatures, which will counterbalance the decrease in reflected shortwave associated with lower CFs and the thinner optical depths associated with decreased IWC and LWC in the E5 simulation. Vertical motion within the newest E5 simulation is greatly weakened over the EP-ITCZ region, potentially due to atmospheric loading from enhanced ice particle fall speeds. Comparatively, E5 simulated upward motion in the INDO-WP is stronger than its predecessors. Changes in the E5 simulation have resulted in stronger/weaker upward motion over the ocean/land in the INDO-WP region in comparison with both the C5 and P5 predecessors. Multimodel precipitation analysis shows that most of the GCMs tend to produce a wider ITCZ with stronger precipitation compared to GPCP and TRMM precipitation products. E5-simulated precipitation decreases and shifts Southward over the Easter Pacific ITCZ, which warrants further investigation into meridional heat transport and radiation fields